View full sizeThis undated handout file photo provided by the Agriculture Department shows an
aedes aegypti mosquito on human skin. Old mosquitoes usually spread disease, so Australian
researchers figured out a way to make the pests die younger - naturally, not poisoned.
Scientists have been racing to genetically engineer mosquitoes to become resistant to diseases
like malaria and dengue fever that plague millions around the world, as an alternative to mass
spraying of insecticides. (AP Photo/USDA, File)

LANSING — State health officials are urging people to protect themselves and livestock from being bitten by mosquitoes after confirmation that a deadly mosquito-borne virus had killed at least five horses in Southwest Michigan as of Monday.

The horses were killed by Eastern Equine Encephalitis, a viral brain disease, and tests on additional horses are pending, officials said.

“We know of an additional three with test results pending, and there may be others that haven’t yet come to state’s attention,” State Veterinarian Steven Halstead said Monday.

“If we see more than three cases in a cluster we consider that an outbreak. This is an outbreak.”

EEE is spread by mosquitoes from infected birds to horses and other equines, such as mules, and to deer. It can also infect humans, but has not been found in people in Michigan this season, said James McCurtis, spokesman for the Michigan Department of Community Health.

Vaccination is available and strongly urged for horses, though it provides no guarantee, Halstead cautioned. Preliminary reports suggest that two of the dead horses may have been vaccinated, he said.

Michael Kaufman, research and Extension specialist in entomology at Michigan State University, said limiting exposure to mosquitoes that carry the disease is an important step for people and animals alike.

Mosquitoes have been plentiful this year, with hot weather and frequent rains resulting in ideal breeding conditions for most species, Kaufman said. On Monday, Kaufman was alerting colleagues who work in mosquito-infested areas in Southwest Michigan to take special care to use repellent and take other steps to avoid being bitten.

State officials echoed that warning to the population at large in a statement released jointly by the departments of agriculture and community health Monday.

“One bite from an infected mosquito can lead to severe and possibly life-altering illness,” said Janet Olszewsk, director of the Michigan Department of Community Health.

In healthy adult humans, EEE begins with flu-like symptoms of fever and headache, but the disease can overwhelm the central nervous system of susceptible individuals, usually the young, elderly, or those whose immune systems have been weakened, Kaufman said.

The confirmed diagnosis of EEE in horses came Monday from the Michigan State University Diagnostic Center for Population and Animal Health. A 3-month-old Percheron filly from Calhoun County and a 12-month-old Arabian horse from Barry County tested positive; MDA was notified by the National Veterinary Services Laboratories on July 20 of a third case, in a four-year-old mixed breed mare from Cass County.

Two more horses, in St. Joseph and Barry counties, tested positive as well, Halstead said.

Although birds harbor the virus, allowing it to be spread by mosquitoes that bite them, the disease generally does not cause illness in songbirds, though it can be deadly to pheasants, ostriches and emus, Halstead said.

Eastern Equine EncephalitisBecause of the high mortality rate for horses and humans, EEE is regarded as one of the most serious mosquito-borne diseases in the United States.Below are tips for preventing mosquito-borne diseases.For people:

Avoid mosquito bites: Use insect repellent when outdoors, especially from dusk to dawn. Look for EPA-labeled products containing active ingredients, such as DEET, Picaridin (KBR3023), or oil of lemon eucalyptus (p-menthane 3,8-diol). Apply more repellent, according to label instructions, if mosquitoes start to bite.

Mosquito-proof homes: Fix or install window and door screens and cover or eliminate empty containers with standing water where mosquitoes can lay eggs.

For horses:

Protect horses with licensed vaccines, given annually, against EEE, recommended for all horses in the U.S. It’s not too late this year to vaccinate horses.

Use approved insect repellents to protect horses.

If possible, put horses in stables, stalls, or barns during the prime mosquito exposure hours of dusk and dawn.

Eliminate standing water and drain water troughs, and empty buckets at least weekly.

Sources: Michigan Department of Community Health, Michigan Department of Agriculture

For more information on the human health impact of EEE: Centers for Disease Control and Prevention (CDC) web site at www.cdc.gov/ncidod/dvbid/arbor/eeefact.htm.For more information about EEE in horses, consult your local veterinarian or contact MDA’s Animal Industry Division at 517-373-1077; or visit the MDA website: www.michigan.gov/mda.